Skeletal system · Head and neck
Mental foramen !
The mental foramen is an opening on the front of the lower jaw below the premolars, where the nerve for feeling in the lower lip and chin comes out.
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What it is
An opening on the front of the lower jaw below the premolars.
What it does
The mental nerve comes out here (feeling of the lower lip and chin).
Key facts
- Where
- Mandible, below the 2nd premolar
- Function
- Transmits the mental nerve and vessels (lower lip and chin)
Relations
- Contents
- Mental nerve, the end branch of the inferior alveolar nerve, with the mental artery and veins; the incisive branch stays inside the bone for the front teeth
- Course
- The inferior alveolar nerve runs forward in the mandibular canal; below the premolars it splits, and the mental nerve may run a little forward (anterior loop) before turning up and back out of the foramen
- Superficial
- Depressor anguli oris and depressor labii inferioris; the nerve fans out beneath them to the skin of the chin and the lower lip and its mucosa
- Above
- Roots of the premolars, most often the second premolar
How to find it
In an adult with teeth it lies about midway between the gum margin and the lower border of the mandible, below the second premolar, on the vertical line through the pupil; firm pressure there may be tender. Inside the mouth it lies deep in the vestibule below the premolars.
On imaging
A panoramic radiograph shows it as a round dark spot near the premolar roots that can be mistaken for a lesion at the root tip; cone-beam CT maps it and the anterior loop before implants.
Clinical notes
- Mental nerve block at the foramen numbs the lower lip and chin on one side; it does not reliably numb the teeth, which are supplied by the incisive branch
- «Numb chin syndrome»: new numbness of the chin and lower lip without trauma or a dental cause can be the first sign of metastatic cancer or lymphoma
- Implant placement, premolar surgery and chin (genioplasty) operations are planned around the foramen to avoid lasting numbness
Anatomical variants
- Position ranges from below the first premolar to below the first molar; below the second premolar, or between the two premolars, is most common
- Accessory mental foramina, usually smaller and behind the main one, in a minority of people; they may carry branches a block misses
Development
In the newborn it lies near the lower border, under the developing tooth buds; it moves up to mid-height as the alveolar process grows.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Where is the mental foramen in an adult with teeth?
Below the second premolar, about midway between the gum margin and the lower border of the mandible, on the vertical line through the pupil.
Which nerve exits the mental foramen, and what does a block there numb?
The mental nerve, end branch of the inferior alveolar nerve; the block numbs the lower lip and chin but not reliably the teeth.
What is «numb chin syndrome»?
New numbness of the chin and lower lip in the mental nerve territory without trauma or a dental cause; it can be the first sign of metastatic cancer or lymphoma.
Why can a denture press on the mental nerve in a person without teeth?
The alveolar bone shrinks, so the mental foramen comes to lie near the top of the jaw.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- foramen mentale TA2 845
- Official Spanish (DeCS)
- Agujero mentoniano
- English (TA2)
- Mental foramen
Sources: Terminologia Anatomica (TA2); Anatomy, Head and Neck, Mental Nerve; Anatomy, Head and Neck, Mandible.
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Representative model, for educational purposes only.